1. Field of the Invention
The invention relates to the field of processes for assembling porous materials by adhesive bonding using adhesives. It is in particular applicable to cores for coils or transformers, for example for electrical power supplies of equipment installed onboard an aircraft or satellite, the cores of which are made of ferrite. As is known, these cores are intended to increase the local magnetic permeability in the vicinity of the windings, typically of coils or transformers.
2. Discussion of the Background
One example of a ferrite former used for such embodiments is represented by way of indication in FIG. 1. This figure represents a perspective half-view.
The ferrite piece 1 represented in FIG. 1 includes, around an axis XX' of revolution, a central core 2 of cylindrical shape and a peripheral ring 3, concentric with the central core. The peripheral ring includes two openings 4, 5, intended to make it possible for the wires constituting a winding (not shown) to be passed through. The central core 2 and the peripheral ring 3 are joined by a base 6. A hollow space 7, between the central core and the peripheral ring, allows the winding to be inserted. When the winding is in place, a second ferrite piece, which is symmetrical with the piece represented in FIG. 1, with respect to a plane perpendicular to XX', is placed against this piece represented. The magnetic circuit of the winding is then complete and closed.
One currently known process for joining the two ferrites, and thus assembling what is referred to as the "pot", is a process by adhesive bonding using an epoxy resin, for example araldite (registered trade mark of CIBA GEIGY).
A bead of adhesive is deposited between the two pieces, at the external periphery of the peripheral ring.
Such a process is generally satisfactory both from the electrical point of view, since the air gap is fairly small, and from the mechanical point of view, since assembly is solid and reliably produced.
Such assembly does, however, have two major drawbacks. On the one hand, it requires the use of a resin and a hardener, which implies prior preparation, and on the other hand it results in the presence of a peripheral assembly bead. This bead constitutes a protuberance which increases the overall diameter of the pot. This increases the size required for the pot insertion, which overall increases the volume and therefore the weight of the circuits into which the pots are then incorporated.
In order to reduce the size of these pots, the Applicant Company has envisaged replacing the external epoxy resin bonding bead by adhesively bonding the faces of the two parts of the pot to be assembled.
It was not possible to use epoxy resins, for example, for this adhesive bonding because the films deposited are too thick and produce air gaps which are too large, in excess of 150 .mu.m, which impairs the electrical properties of the circuit.